Prevalence and coprevalence of modifiable risk factors for upper digestive tract cancer among residents aged 40–69 years in Yangzhong city, China: a cross-sectional study oleh Ru Chen, Xi Wang, Xiang Feng, Qin Zhou, Zhao-Lai Hua, Ai-Wu Shi, Tong-Qiu Song, Dong-Fu Qian, Gui-Qi Wang, Wen-Qiang Wei, Jin-Yi Zhou, Jie-Jun Wang, Gang Shao